DOC Update release dates

Author: jnothman

doc/index.rst

@@ -207,7 +207,9 @@
                     <li><em>On-going development:</em>
                     <a href="/dev/whats_new.html"><em>What's new</em> (Changelog)</a>
                     </li>
-                    <li><strong>Scikit-learn 0.21 will drop support for Python 2.7 and Python 3.4.</strong>
+                    <li><strong>Scikit-learn from 0.21 requires Python 3.5 or greater.</strong>
+                    </li>
+                    <li><em>May 2019.</em> scikit-learn 0.21 is available for download (<a href="whats_new.html#version-0-21">Changelog</a>).
                     </li>
                     <li><em>March 2019.</em> scikit-learn 0.20.3 is available for download (<a href="whats_new.html#version-0-20-3">Changelog</a>).
                     </li>
@@ -221,8 +223,6 @@
                     </li>
                     <li><em>July 2017.</em> scikit-learn 0.19.0 is available for download (<a href="whats_new/v0.19.html#version-0-19">Changelog</a>).
                     </li>
-                    <li><em>June 2017.</em> scikit-learn 0.18.2 is available for download (<a href="whats_new/v0.18.html#version-0-18-2">Changelog</a>).
-                    </li>
                     </ul>
                 </div>
 

doc/whats_new/v0.21.rst

@@ -7,7 +7,7 @@
 Version 0.21.0
 ==============
 
-**In development**
+**May 1, 2019**
 
 Changed models
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